Delay Send holds all outbound messages for up to one minute (default is 5 seconds) before sending them out, giving you a window to recall the message. Messages sent using delay send will appear in the Sent Items folder and will have an indicator on them until they reach the send time.
To change the duration or disable this feature:
Step 1: Go into Settings from the More dropdown menu
Step 2: Locate the Email tile and select a setting from the Delay Send In Seconds dropdown
Options are: Disabled, 5, 15, 30, 60 (seconds)
Step 3: Click Save
To recall a message after you click Send, click Undo Send at the bottom of the message column and it will put the new email immediately into the Drafts folder. Here, you can then edit, change, or otherwise delete the message before it's actually sent.
You can also click Send Now from the Send drop down to bypass the Delay Send feature to send the email immediately.